1. Technical Field of The Invention
This invention relates to a magnetostatic wave device and, more particularly, to the same device which includes a ferrimagnetic base such as an YIG (yttrium, iron, garnet) thin film and, is used, for example, for a filter or an oscillator resonator with application of direct current magnetic field to the ferrimagnetic base in the direction perpendicular to its surface.
2. Description of The Prior Arts
One example of conventional surface magnetostatic wave devices which constitutes a background of this invention is disclosed in Japanese Patent Provisional Publication No. 143819/1980.
FIG. 7 is a perspective view showing one example of such conventional magnetostatic wave devices. This magnetostatic wave device 1 includes an YIG thin film 2. The YIG thin film 2 is formed on one main surface of a GGG (gadolinium, gallium, garnet) substrate 3. Furthermore, an input antenna 4 and an output antenna 5 are provided on the YIG thin film 2 and they are spaced apart. Each one end of these antennas 4 and 5 is grounded and each other end of them is connected to an input terminal 6 and an output terminal 7 respectively.
Such a magnetostatic wave device is used under the condition which a direct current magnetic field is applied to the YIG thin film surface in the direction perpendicular to its surface. When this magnetostatic wave device is used as a resonator, a resonance frequency of the resonator may be varied by varying the direct current magnetic field intensity.
However, such a conventional magnetostatic wave device has bad selectivity at a resonance frequency and large insertion loss, that is, a small Q-value. In addition, the conventional magnetostatic wave device has also bad spurious mode separation.